This invention relates to analog signal processing, and more particularly to transceivers. This invention further relates to the transceiver and components thereof described and claimed in the following U.S. patent applications filed of even date with and assigned to the assignee of the present invention: U.S. Ser. No. 791,611 entitled "A Digitally Transmitting Transceiver" by Edward R. Caudel and William R. Wilson; U.S. Ser. No. 791,629 entitled "A Clarifying Radio Receiver" by Michael J. Cochran and Edward R. Caudel; U.S. Ser. No. 791,449 entitled "An Automatically Clarifying Radio Receiver" by Michael J. Cochran and Edward R. Caudel; U.S. Ser. No. 791,254 entitled "A Computer Controlled Radio System" by Michael J. Cochran and Edward R. Caudel; U.S. Ser. No. 791,614 entitled "A Charge Transfer Device Radio System" by Michael J. Cochran; U.S. Ser. No. 791,253 entitled "A Transceiver Capable of Sensing a Clear Channel" by Jerry D. Merryman, et al; U.S. Ser. No. 791,265 entitled "A Signal Strength Measuring Transceiver" by Edward R. Caudel; U.S. Ser. No. 791,256 entitled " A Highly Selective Programmable Filter Module" by Michael J. Cochran and Edward R. Caudel; U.S. Ser. No. 791,616 entitled "A Dual Processor Transceiver" by Edward R. Caudel, William R. Wilson and Thomas E. Merrow; U.S. Ser. No. 791,264 entitled "An Electronic Phase Detector Circuit" by Michael J. Cochran. A transceiver has a transmit mode of operation and a receive mode. In a receive mode, the transceiver receives radiated electronic input signals comprised of a plurality of non-overlapping frequency bands, filters one of the bands from the plurality, frequency shifts the one band from radio frequencies to a lower frequency, and converts the filtered band to audible sounds. The input signals may be amplitude modulated (AM) or single sideband (SSB) signals as an example. Antenna means receive the radiated input signals. Filtering devices are included in the transceiver to select one of the bands from the plurality. Mixing devices are included to frequency shift the selected band, and a demodulator device is included to demodulate the selected band. Similarly, in a transmit mode, a transceiver modulates electrical signals having audio frequencies, frequency shifts the modulated signals to radio frequencies of a selectable channel, and radiates the radio frequencies via an antenna.
A plurality of clocking signals having selectable frequencies are required to implement the above-described transmit and receive operations. For example, the mixing devices which are operable in the receive mode, frequency shift the radiate input signals such that a selected band is aligned to predetermined frequencies in response to the frequency of one of the clocking signals. Similarly, the demodulator device, which is utilized in the receive mode, demodulates in response to the frequency of another clocking signal when single sideband signals are received. Additionally, the mixing devices, which are active in the transmit mode, frequency shift signals from audio frequencies to radio frequencies in response to the frequency of another clocking signal.
In the past, at least two independent reference frequency oscillators were required to generate the clocking signals that the transceiver needed. In some systems, one of the oscillators generates one reference frequency which produces clocking signals for the receive mode of operation; while a second oscillator generates another reference frequency which produces signals for the transmit mode of operation. By comparison, the present invention generates both the transmit clocking signals and the receive mode clocking signals from a single fixed reference frequency. Thus, the present invention has the advantage of eliminating some components which other transceivers previously required.
Another advantage of the presently-described invention is that the clocking signals of the transmit mode and receive mode are synchronized to each other. The synchronization results from the fact that all clocking signals in the described invention are multiples of a single reference frequency. That is, each clocking signal has a frequency of the form K1/K2 times the reference frequency where K1 and K2 are selectable integers. Thus, the difference in frequency between any two clocking signals in the disclosed transceiver is solely dependent upon the integers K1 and K2. By comparison, the difference in frequency of two clocking signals of prior art transceivers is dependent upon the tolerance in the frequency of oscillation of the multiple reference frequency oscillators.
Accordingly, it is one object of the invention to provide an improved transceiver.
It is another object of the invention to provide a transceiver having clocking signals which are all synchronized to each other.
Another object of the invention is to provide a transceiver having clocking signals which are derived from a single reference frequency.
Still another object of the invention is to provide a transceiver having clocking signals whose difference in frequency is independent of the frequency tolerance of multiple oscillators.